The present invention relates to processes for simultaneously rinsing and drying substrates. More particularly, the present invention relates to an ultra clean process and apparatus for simultaneously rinsing and Marangoni drying a semiconductor substrate.
As semiconductor device geometries continue to decrease, the importance of ultra clean processing increases. Aqueous cleaning within a tank of fluid (or a bath) followed by a rinsing bath (e.g., within a separate tank, or by replacing the cleaning tank fluid) achieves desirable cleaning levels. After removal from the rinsing bath, absent use of a drying apparatus, the bath fluid would evaporate from the substrate""s surface causing streaking, spotting and/or leaving bath residue on the surface of the substrate. Such streaking, spotting and residue can cause subsequent device failure. Accordingly, much attention has been directed to improved methods for drying a substrate as it is removed from an aqueous bath.
A method known as Marangoni drying creates a surface tension gradient to induce bath fluid to flow from the substrate in a manner that leaves the substrate virtually free of bath fluid, and thus avoids streaking, spotting and residue marks. Marangoni drying uses relatively small amounts of IPA. Specifically, during Marangoni drying a solvent miscible with the bath fluid is introduced to a fluid meniscus which forms as the substrate is lifted from the bath or as the bath fluid is drained past the substrate. The solvent vapor is absorbed along the surface of the fluid, with the concentration of the absorbed vapor being higher at the tip of the meniscus. The higher concentration of absorbed vapor causes surface tension to be lower at the tip of the meniscus than in the bulk of the bath fluid, causing bath fluid to flow from the drying meniscus toward the bulk bath fluid. Such a flow is known as a xe2x80x9cMarangonixe2x80x9d flow, and can be employed to achieve substrate drying without leaving streaks, spotting or bath residue on the substrate.
A conventional Marangoni drying system is disclosed in European Application number 0 385 536 Al, titled xe2x80x9cMethod and Arrangement for Drying Substrates After Treatment In a Liquid.xe2x80x9d The ""536 System submerges a substrate in a fluid bath. A vapor (e.g., an alcohol vapor) miscible with the bath fluid is mixed with a carrier gas and then passed over the surface of the fluid bath via a plurality of nozzles. The vapor mixes with the fluid bath along the surface thereof, lowering the surface tension of the fluid bath. A fluid meniscus forms along the air/liquid/substrate interface as a substrate is lifted from the fluid bath. This meniscus is formed from the surface layer, and thus has a lower surface tension than does the bulk bath fluid. Accordingly, fluid flows from the surface of the substrate to the bulk bath fluid, leaving a dry substrate surface. Although apparatuses such as that disclosed in the ""536 Application effectively remove fluid from the substrate, they consume a considerable amount of fluid because the bath fluid cannot be filtered and recirculated to remove drying vapor therefrom. Thus, the bath fluid must be replaced frequently to maintain a sufficient surface tension gradient at the drying meniscus. Further, considerable time is required to transfer a substrate from the cleaning to the rinsing bath, or to replace bath fluid.
Accordingly, a need exists for an improved method and apparatus that quickly and effectively cleans, rinses and dries a substrate, eliminating not only streaks, spotting and bath residue marks, but also conserving rinsing fluid consumption and reducing the overall time required for the cleaning, rinsing and drying process.
The present invention provides a method and apparatus for simultaneously bath cleaning, rinsing and Marangoni drying a substrate. The invention is advantageously designed to increase system throughput and reduce fluid consumption. The invention comprises an apparatus for drying a substrate, the apparatus comprising:
a first linear nozzle (i.e., a nozzle having an elongated aperture capable of spraying a line of fluid so as to wet a relatively large portion of the substrate, as compared to a single standard nozzle);
a fluid supply coupled to the first linear nozzle;
a second linear nozzle positioned proximate the first nozzle such that drying vapors therefrom affect the fluid sprayed from the first linear nozzle to create a Marangoni drying effect;
a drying vapor source coupled to the second linear nozzle; and
a mechanism for passing the substrate past the first and second linear nozzles within an operative distance such that the substrate is dried by the Marangoni drying effect. Alternatively, the first and second linear nozzles can be replaced by a first and second linear array of fan type nozzles. As a further alternative, the drying vapor may be supplied passively, rather than through one or more nozzles.
The inventive nozzle system may be used with a number of conventional or inventive apparatuses to further enhance clean/dry levels and system through-put. In a first embodiment, the inventive apparatus comprises a cleaning fluid tank, a lifting mechanism operatively coupled to the tank for lifting substrates from the tank, a drying vapor source and a rinsing fluid source positioned to supply rinsing fluid to the surface of a substrate as the substrate is lifted from the tank. The rinsing fluid contacts the substrate forming an air/substrate/rinsing fluid interface preferably in the form of a meniscus. The drying vapor source is positioned to supply drying vapor to the air/substrate/rinsing fluid interface, directing drying vapor to a point 1-5 mm above the air/substrate/rinsing fluid interface. Both the rinsing fluid source and the drying vapor source preferably comprise either an array of fan-type nozzles or a single line-type nozzle. However, the drying vapor source may also comprise a passive source such as a vessel filled with the drying fluid positioned along the passage from the rinsing fluid source to the drying chamber so that drying vapors diffuse to the air/substrate/rinsing fluid interface. The rinsing fluid nozzles and the drying fluid nozzles may extend along both the frontside and the backside of the substrate and thereby simultaneously rinse and dry both sides of the substrate.
The active supply of drying vapors via drying vapor nozzles provides tight control over the concentration of drying vapors at the drying meniscus. Unlike other bath-type Marangoni dryers, the present invention provides a continuous supply of fresh rinsing fluid which, unlike the more stagnant bath fluids, has no drying vapors mixed therewith. Thus, the present invention experiences a larger surface tension gradient between the drying meniscus and the remainder of the rinsing fluid flow. The larger surface tension gradient enhances the speed of Marangoni drying. Most significantly, because less fluid is required to spray the entire surface of a substrate than to submerge the substrate, the use of rinsing fluid nozzles significantly reduces fluid consumption as compared to conventional bath-type Marangoni dryers.
In a most preferred embodiment, the throughput of the inventive cleaning/drying system is enhanced via a two-part tank, having a first portion for receiving and cleaning a substrate and a second portion for rinsing a substrate. The first and the second portion of the cleaning tank are in fluid communication. A drying enclosure which encloses the rinsing fluid source and the drying vapor source is operatively coupled above the second portion of the tank, for receiving substrates therefrom.
Preferably, a shuttle which supports a substrate along the outer edges thereof, receives a first substrate in the first portion of the tank and transports the substrate to the second portion of the tank. Thereafter, the lifting mechanism lifts the first substrate into the drying enclosure, and the shuttle returns to the first portion of the tank. In this manner, the first substrate may be dried within the drying enclosure as a second substrate is loaded into the first portion of the cleaning tank, thus providing greater throughput and a corresponding decrease in processing costs.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.